Changing the position of the rear suspension

[hardtdavid]

On a Sofrider V1, the front end of the rear suspension attaches to the middle anchor hole of three anchor holes underneath the seat. I can imagine that if the suspension attached to the upper hole, the head tube angle would increase---and if the suspension attached to the lower hole, the head tube angle would decrease---, by how much, I do not know. The handling of the bike would change accordingly.

Two questions:

1. Is it advisable/useful to change the position of that rear suspension attachment for the Sofrider? Or would the handling change too dramatically or negatively? What changes in handling/steering feel, etc. would result?

2. If would be OK to change that attachment point, how does one do that? Special tool or bike shop assistance required?

Thanks.

 

[John Zabriskie]

answers to your questions:

#1) If you keep the same rear shock, changing the location of the shock mounting point on the frame would slacken the head tube angle from the stock 68.5° to 67° for the top hole & 66° for the bottom hole (at least on the Sofrider V2.1 frame I have available for reference). This would be useful if you think the steering doesn't have good "feel" or the front end feels "nervous" or "twitchy" when you ride. Slackening the head tube angle increases the fork's trail giving more steering feedback & stability, especially at higher speeds. In the extreme, this would introduce "fork flop", but these hole locations do not yield that drastic a change. It's quite subjective to assess. Additionally, there would be a subtle drop in seat back angle & raising of the bottom bracket height. This might yield some aero benefits, but they'd be relatively minor.

I cannot check out the handling differences the different mounting points introduce, since my riding season is curtailed until the snow melts off the Idaho roads. Perhaps someone in a warmer clime can run this experiment & report the results. What feels different when you vary the shock attachment positions?

Changing the rear shock will have a much more dramatic effect on the handling. For example, I bolted on a Cane Creek AD-10 (which is substantially lighter than the stock unit) & found, after an afternoon of adjusting & tweaking, a wonderful balance of air pressure, rebound & damping. The rear end was almost plush. If you can find a used model any of the air shock variants on e-bay, it might be worth the extra expense. [I only wish the front fork could be tuned & tweaked this way.]

#2) No special tools required to swap the shock mounting point, other than a pair of hex wrenches. No assistance is needed, unless you're not mechanically inclined.

 

[Doug Burton]

I'd be really surprised if you noticed any change at all in the handling with these small changes of angle.

The seating angle and height will change a little, depending on which hole you use and where you set the spring perch on the shock.

If you have a rear rack mounted, make sure the rear tire doesn't hit the rack under rear suspension compression if you lower the rear suspension. This is especially true on V2 frames, where the top tube is already 1" lower than on the V1.

Also, the head angle should be measured with the suspension loaded, i.e. with you sitting on the bike.

Cheers,

Doug

 

[hardtdavid]

John Z., thanks for the reply and experience notes.

I hadn't thought of changing the shock itself. I am not familiar with air shocks (or any other kind) since this is the first suspended bicycle I've ever owned.

Is the stock spring shock kind of crude? What sort of difference would an air shock make? Are they difficult to tune? (I've installed already some nice wide Schwalbe Marathon Supremes on my Sofrider V1, and lowered the air pressure, to get a nice smooth and yet still speedy ride, along with less high-freq vibrations and better handling).

If I were to look for air shocks on eBay as you suggest, what brands or models might I look for to get the weight reduction you are talking about?

Thanks again for the help.

 

[John Zabriskie]

I'm on the road tonight heading to St. George, UT. The internet at the hotel is less than adequate, so we'll see how much of this is posted.

I think the stock Sofrider spring/shock (Kind shock 258) is pretty stiff with it's 850#/in spring rate & as far as I can tell, the damping is frictional; it doesn't seem to be speed sensitive. Plus, it's heavy compared to an air shock. Since you've got the Marathons dialed in, you won't notice as much of a difference with an air shock as I did with the Kenda Kwests pumped up to 100 psi. Adjustability is the key for an air shock; the air pressure sets the spring rate. Early AD-5's, for instance didn't have much, other than the air pressure. Later versions, like the AD-10 had rebound & compression adjusters. For a road bike, air pressure is really what you'll need to play with. The rebound & compression adjustment is really only needed for off-road riding where you get a lot of suspension travel. I like to set the air pressure on the heavy side of plush -- it still handles the smaller bumps well without bobbing too much when you get on & off the power.

There are a number of air shock manufactures out there: Cane Creek, Fox, . . . even Kind Shock makes some. Look in some MTB magazines for reviews or ask some of the techs at your LBS if they've got any "pulls" from someone who's upgraded & what they would recommend.

I recently got a newer Cane Creek Cloud Nine off e-bay that had a 7 1/2" center spacing, an inch longer than the AD-10 shown above. I'm trying it out on the Sofrider -- it changed the head tube angle from ~68° to ~72°. I've only got about 20-miles on it so far (in between snow storms). It seems a little lighter in the steering, but not significantly so. I had to recline the seat some more to compensate for the tilt.

 

[hardtdavid]

Thanks again, John.

I installed the larger diameter Marathons after reading that wider tires would improve handling without any real loss of "speed." With the Kendas I was getting so much "chatter" on high speed descents, that I was never confident of the contact with the road. Now the handling and "road feel" are splendid.

I like the idea of playing with the head angle. I installed 50-559 on the rear and 42-559 on the front take make a small difference on my sofrider. I am looking for a little more feeling of control. The stock setup sometimes feels resistant to steering control, again, at higher speeds.

If I understand you correctly, the main differences switching to an air shock would be 1) adjustable stiffness (rather than the plain "stiff" of the stock spring), and 2) lower weight.

A) how much of a weight difference? Significant enough to consider a switch merely for that benefit?

B) I don't want the ride to become too plush: can an air shock be pumped up fairly stiff?

Also: what did you mean that the stock spring is not "speed sensitive" (implying that an air shock would be)?

Safe travels.

 

[John Tolhurst]

hello hardtdavid,
What air pressure did you run in the Kenda's and what do you run in the Marathons?

 

[hardtdavid]

Hi, John T,

The short answer is: around 35psi in the 50-559 rear, and 50psi in the 42-559 front.

The full story is I bought a used Sofrider two years ago, and replaced the 65psi Kendas with 100psi Kendas; then started getting used to riding the bike on progressively more challenging hills. I almost always ran the tires at 100psi or close to it. I always felt uneasy going downhill at speed, as if the I had no real sense of road contact, especially on anything less than a perfect road surface. I could all the vibrations from the imperfections. (I always do continue pedaling, as you recommend, and I agree, it is necessary to feeling better in control of the bike).

Then I bought another used Sofrider for my wife, and noticed that hers felt much different from mine: solid steering feel even on downhills. I kept trying to figure out the difference. The only discernible difference between the bikes was the 65 vs 100 psi tires---so I started lowering the pressure in my 100psi Kendas, and notice some improvement. Eventually, I was running the 100psi Kendas at 65psi! It made a big improvement in the feel, with no discernible loss of speed. Even then, my bike didn't feel quite as confidence inspiring as my wife's!

Then I read the Bicycle Quarterly article on "tire drop" as an indicator of proper air pressure, based on overall load on each tire. (You've read and commented on my post regarding that article elsewhere in this forum). BQ also has done research showing that for the average rider, wider tires (at the proper tire drop pressure for the rider/bike combination) have rolling resistance and speed comparable to many if not most skinnier tires, and they often improve the handling and comfort on many bikes as well. Some bikes rider better with wider tires. (In other words, their conclusion is tires wider than 1 inch would serve most riders better, offering a more enjoyable ride without compromising speed. But few people looking at a skinny tire next to a wider tire would believe that.)

Of course some riders need the higher pressure in their tires, and always "top off" the tires before a ride---but I think this might be because they need it---a lot of riders weigh more than I do, and the tire loads are greater. I'm pretty low weight (70kg/155lbs), and by the charts, I should be riding at 60psi or below for 1.25 or 1.50 tires to achieve the most efficient tire drop. My experience with the two Sofriders seems to support this. I get a much better ride from the lower pressures.

When I upgraded the wheels on my Sofrider, I opted for Marathon Supreme tires, for their reputation for good road grip, and their lower weight and low rolling resistance. I thought I'd try 50-559 on the rear and 42-559 on the front to increase slightly the head angle, hoping to get slightly zippier steering (I had test ridden one of your super cool Silvio's by this time...).

Based on my weight plus the bike's weight, and an estimate of 55% front-45% rear distribution, I run the rear 50-599 at around 35psi, and the front 42-559 at around 50psi. The difference in handling and road feel is dramatic: the constant "chatter" is gone, even at 30+mph down hill on rough road finishes. The "contact with the road" feel I was looking for is always there.

As an amateur not running a time trial I notice no loss in speed. In fact, by the computer, I am faster. Some of that is the lighter wheels (and the lighter, higher quality tires), but I mention it just to indicate that wider tires don't mean slower here. (I ride in a 16-18mph group these days).

I continue to look for other ways to lower the weight, and to make slight improvements in the handling---thus, my interest in following up on John Z.'s switch to a different rear shock. But make no mistake, I love the way my Sofrider rides as it is now. I've completed a century with it (actually, before the switch to new wheels and tires), and I noticed how at 80 miles everyone else was aching and complaining, but I still felt great!

David Hardt


You know, I test rode the Silvio, and I'm sure the LBS fellow topped off the tires. I wonder what it would have felt like to me if I had ridden it at the pressure more suited to my low weight?

 

[John Zabriskie]

David, thanks so much for originally posting the link to the "tire drop" article. I'm passing it on to all the cyclists I know.

I'm enjoying the balmy temperatures in southern Utah & won't be home until late tomorrow night, so I can't get you the weights of the various rear shock options. I'll update the weight info sometime Monday evening. The guy who built the "SilvRider" indicated the AD-5 he used was half the weight of the stock shock. My opinion is that converting just for the weight is not an adequate reason alone (unless you're a weight weenie). For me, the reason was to be able to adjust the spring rate via the air pressure. [I still haven't played around with the damping & rebound settings since I was primarily after the spring rate tuning.]

The air shock can be pumped up quite stiff; in my case, approx. 200 psi is almost no suspension, 185 is where I'm running now & 160 is too cushy. Bear in mind I'm approx. 200#. You would undoubtedly need much less pressure to achieve a similar feel. Since you've achieved such a transformation in the handling with your tire experiments, I wouldn't put the rear shock conversion as a high priority. You're already 90% there & it won't add that much.

The "speed insensitivity" comment about the stock shock refers to the lack of any real damping I seen. Loosen the rear spring completely & take the shock off the bike so you can play with it. Compress & extend the shaft without any spring pressure -- it moves freely without any resistance regardless of how fast or slow you move the shaft.

 

[John Tolhurst]

The great misconception about tires is that the tire tread bites into the road, whereas in truth it is the tire conforming to the road, it is the road surface doing the biting. Once you understand that, then you can see why on rocky stony surfaces we need to drop pressure to keep adequate area contact and adequate feel. Too high and the bike literally bounces over each stone, rather than the tire accepting each stone by deformation.

Another alluring misconception is that wider profile tires have a large contact patch. They don't, not for the same pressure. They may have a broader elliptical contact path and they might therefore have a greater chance of always passing over at least some good surface - but the surface area is the same at 50 psi for the same load being carried on that tire. i.e. for a 50lb load, a 50psi tire will have a contact area of one square inch.

Wider profiles allow lower pressure with less chance of rim contact with the road, resulting in 'snake bite' punctures where the rim pinched the tube within the tire.

See my http://www.cruzbike.com/forums/viewtopic.php?f=10&t=183&p=8732&hilit=keating#p1373 Keating Road ride report.

On the rides that I am doing at present on the Vendetta prototype, the surfaces are pretty good, smooth asphalt. The harder the tires, the faster I go. Ruts or curb drops or bumps I navigate by bridging from the small of my back through to my feet, which helps a good deal.

Technically challenging high speed gravel descents need to be made with a vertical head position and a seat which is not too reclined, so you can lean forward and liberate the legs as counterweights when the rear looses it. Ah, but I digress ...

 

[John Zabriskie]

On my kitchen scale, the stock Kind Shock 258 weighs 504 g, whereas the Cane Creek AD-10 weighs 248 g. If the shocks had the same performance, I wouldn't think it would be reason enough to change. However, since the air shock is so adjustable, the performance benefits are reason enough for the change & the drop in weight is just "icing on the cake."

On a related note, I remember reading a posting years ago from Bob Stuart (of Car Cycle fame) in which he explained the effects of having different spring rates front & rear. He explained that if the rear spring rate was too "soft" compared to the front, the ride motions could make the rider physically ill. I don't know what the front fork spring rate is on the Sofrider, but it seems like it needs to be fairly high, since the travel is relatively small (compared to a mountain bike). Therefore, I think that is why the rear shock spring rate is fairly stiff, to ensure it is the same or higher than the front rate.

On my air shock, I 1st adjust the spring pressure so it's kind of "bouncy" when I sit on the Sofrider. Then, I increase the pressure in 5 psi increments & test ride. I also look at the shock to see how much of the available travel I've used. I normally run the sag at 20 to 25% of the travel. Based on the "tire drop" article, I've adjusted the tire pressures downward some. This has helped with isolating chipseal vibration from both tires. I can then run a little firmer shock pressure if the road surfaces are rather potholed & broken up.

 

[hardtdavid]

To John Z.

Yes, isn't proper "tire drop" pressure amazing?

Well, for the average bike and rider, anyway. Actually, even though John T. says he goes faster the higher he pumps the tire on the Vendetta, that could be "proper pressure" too, if the Vendetta's tires are of the slenderest variety. According to the "tire drop" literature and charts, the super thin tires require super high pressures for all but the lightest of riders. "Tire drop" is not always about lower pressure, that is. In fact, one foot note says explicitly that some riders may not be able to pump their super thin tires high enough for their particular wheel loads, and should go to a wider tire width.

I've also read recently that some of the faired lowrider record seekers are experimenting with wider tire widths for lower rolling resistance since air resistance is moot for them. A rounder contact patch has something to do with it.

John, is the "stock Kind Shock" for the V2 or the V1 Sofrider? I have a V1 by the way. I can't see any brand name on the spring or shock body.

Does the "so adjustable" nature of the air shock apply to a Cane Creek AD-5, or just the AD-10 style enough to make "performance benefits" still worth a switch? I found an AD-5 for $90 plus S/H---reasonable price?

Thanks so much for all your advice and experiences.

 

[John Zabriskie]

Since I'm a big guy riding on less than ideal surfaces, i always opt for wider tires, if possible.

The shock I measured came off a V2. I've not got access to a V1.

The adjustablility comment applies to any air shock -- since the spring rate is a direct function of the air pressure. The AD-5 has limited compression/rebound damping adjustability (I think it's a factory-adjusted thing), but you'll still be able to play with the spring rate.

As for $90? That's really a personal thing -- implied value & that sort of thing. Do you feel it would be worth $90 to you? As a point of reference, the new Cloud Nines are $345 from the Cane Creek website, while I've seen them on e-bay for $225. I haven't seen an AD-5 on e-bay for many years, since they've stopped production. However, the seal kits are still readily available, in case you need to rebuild it.

 

[hardtdavid]

To John T.

Thanks for the "rocky road" advice. I've tried the stock Sofrider on a trail, but the tires were too slick for a lot of the trail. I seem to remember a ride report of yours on a rather gravelly ride with a Sofrider. I was impressed with how low you ran the tire pressure to make the trail rideable. (maybe that's the Keating Road one.) I'm enjoying road riding for now, but I think it will be fun to put some knobbies on the old rims, lower the pressure, and try that trail again.