Adjusting chain tension / changing wheel base?

Related:
Create New Tag

6/4/2018 2:37 PM

Sorry in advance for this question...

Does adjusting the chain tension by lengthening the wheelbase an 1/8" or 1/4" make a significant difference in how the bike handles?

I've heard small adjustments can make the bike feel different, but how much of a change do you need to make before you would notice an appreciable difference?

|

6/4/2018 2:42 PM

I dont notice on the dirtbike AS much, but 1/4” on my street bike is a pretty significant difference in turning ability.

|

6/4/2018 3:04 PM

Depends how sensitive you are. 1/4-1/2 will make a difference for sure.

|

6/4/2018 11:38 PM

I think McGrath back in the day used to run his chain all the way back... I believe I read that somewhere..

|

6/5/2018 12:41 AM

Moving the rear wheel forward/backwards in the swingarm alters the front/rear weight bias, as well as the wheel base, both of which effects stability, cornering, front/rear grip.

It also changes the amount of leverage on the rear shock, having the rear wheel all the way back will make the shock softer, further forward makes it stiffer.

When you put on a new chain next, add an extra link and see if you can tell the difference with the rear wheel far back in the swingarm. If you don't like it, simply remove the extra link and return to a more centered position.
You can also adjust it by changing your sprocket sizes, but this is more costly and effects your final gear ratio.

|

@russ_69

6/7/2018 6:51 AM

RussB wrote:

Moving the rear wheel forward/backwards in the swingarm alters the front/rear weight bias, as well as the wheel base, both of which effects stability, cornering, front/rear grip.

It also changes the amount of leverage on the rear shock, having the rear wheel all the way back will make the shock softer, further forward makes it stiffer.

When you put on a new chain next, add an extra link and see if you can tell the difference with the rear wheel far back in the swingarm. If you don't like it, simply remove the extra link and return to a more centered position.
You can also adjust it by changing your sprocket sizes, but this is more costly and effects your final gear ratio.

^ ^ ^ ^ ^ THIS... ! !

It's amazing what small changes in wheelbase can do to the personality of a bike even while adjusting other things so that the wheel base is changed without affecting other things like effective rake, sag and shaft speed in the shock.

Most people only focus on what changing the rear wheel position will do to the head angle / rake of the machine. And yes, If you move the rear wheel without making a change to shock spring preload it WILL change the effective angle that the forks attack the ground (not the actual head angle/rake of the frame). I often see people trying to improve the behavior of the front end by moving the rear wheel forward in the chassis, this does sometimes work for what you're looking for...... BUT...

....Here's a different approach to the situation from my personal experience and results that is counter intuitive to most people The front wheel on my YZ125 has always been a mythical creature. I've always heard of legends and lore that there is a front wheel on my bike. I've even caught a glimpse of it here and there if I look at it from the right angel while it's on the stand. But I'll damned if I could tell it was there when riding the machine. No feel of the front end what so ever, no traction. If I wasn't wagging the rear tire around like a speedway racer the bike would not turn. Forget about the front tire holding a deep rut without sitting on the fuel cap. I tried all manners of things aimed at changing the effective head angle through sag, spring rates, fork oil levels and shortening the rear wheel base. Never quite got there.... But, I added links to the chain and move the wheel as far back as I could (maybe 3/8in difference) and increased the preload to maintain sage level... Whole new world. My front tire came out of the darkness. I could feel the front tire, turning improved, confidence in the front end improved, lap times dropped. I experimented with this approach on 2 other YZ riders that were struggling with similar feel/traction issues, their lap times decreased as well. I get that body weight and riding style / skill has a huge impact on what approach may work best.

Ultimately for me, with the longer wheel base, it meant a tiny jump up in rear spring rate to maintain free sag with a high race sage and a few clicker changes. Amazing what a small change in only the wheel base will do to the personality of a bike.

|

6/7/2018 7:17 AM

Interesting read ^

Same story with me.... I added a link to the chain on my 15 RMZ450, moving the rear wheel right to the back of the swingarm slot, and all of my front end related handling issues were solved.

My RMZ suffered from a lazy and pushy front end, which was at its worst on hardpack/slick terrain. By moving the rear wheel back, it added weight to the front and hey presto.... accurate and responsive front end.

I did have to stiffen the rear to compensate. It became a little wallowy with poor hold up and sat lower in the stroke.

I got the incentive to lengthen the chain from noticing that nearly every Pro that's ridden the RMZ450 has had the rear wheel slammed right back in the swingarm, most notably Barcia who had his so far back that the JGR boys modified the chain guide to suit.

|

@russ_69

6/7/2018 10:02 AM

I would say the average Joe couldn't feel the difference between all the way back vs. all the way forward.

|

6/7/2018 2:05 PM

I agree. Most people also can't tell the difference in fork offsets either.

(Off topic)
The solution ultimately for my bike, weight and riding style was to reduce the fork offset from the stock 25mm down to 22mm. I did this by fitting 2014 YZ250F triple clamps to a 2001 YZ125 frame. (I know, "that can't be done...blah blah blah" I pressed in a different steering stem, machined different wheel spacers, new brake hanger and I had to have the upper clamp machined to fit the OD of the 2006, the upper is smaller than the lower on the 2014's -'15ish )

That 3mm reduction in offset (big change) increased the trail. Moves the front wheel rearward in relation to the bike and therefore more weight on the front tire, hence more traction and therefore more actual results from turning the front wheel. Increasing trail also adds weight to the feel of the steering, This gave me more tactile feedback of what the front wheel was actually doing instead of the light, nebulous feeling that it used to have.

This was another counter intuitive example of how to improve the turning ability of a bike. The reduction in offset / increased trail is theoretically slowing the steering geometry of the bike, but with increased weight and feel it significantly improved real life effectiveness of the steering. It's no wonder why bikers of all sorts will argue over this topic to the death. haha.

Ian

|

6/7/2018 2:33 PM

Thanks to everyone for replying!

|

6/7/2018 5:19 PM

mxtech1 wrote:

I would say the average Joe couldn't feel the difference between all the way back vs. all the way forward.

You could add a foot to the back of my swingarm, Hayabusa-style, and I'd probably never notice. w00t laughing

|

Braaapin' aint easy.

6/9/2018 9:26 AM
Edited Date/Time: 6/9/2018 11:57 AM

I don't notice a difference in bike handling just due to chain tension, but i definitely notice it by adding 2 links to the chain. As others have said, it makes the bike more stable, but also softens the rear shock a touch since it now has more leverage, and also adds weight to the front end since the front end. All 3 of these things need to be compensated for with clicker adjustments, or in my case i had to adjust the pressures in my SFF TAC slightly to get a similar feel.

|