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Increase ride height or reduce wheelbase length

13K views 30 replies 12 participants last post by  Elk 
#1 · (Edited)
Went -1 with front sprocket/520 conversion. The wheelbase got longer (~5mm). I also went up from 190 tires to 200.

The bike is a bit harder to turn in. I asked some racers about having longer wheelbase. They said it's more stable and better overall. But if I'm about faster turn in I should remove one link from the chain. A suspension guy suggested increasing rear ride height (flip a bolt on rear shock) before I remove a link from the chain.

What do you suggest; remove a link from the chain or just increase ride height? Both?

As you can see in pic, my axle is all the way back.
 

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#5 · (Edited)
I have 120 link chain I can only remove 1 link, if I remove more, chain won't have enough slack. Removing 1 link will make wheel base a tad shorter.

What's wrong with removing just 1 link?

I know @d40 removed one link. Wonder how is that working for him.

@DrIoannis I ride both street and track. Some of the tracks I ride are smaller with fast turn in, others are not. I'm not racing, just need a balanced setup that fits most, it does not have to be perfect.
@Tahoebrian5 +1 on rear will make bike wheelie more and reduce top speed more. I'm pretty happy with -1 in front. Would rather not touch rear. If I know what I know now, I would have kept the front OEM gearing, did +2 on rear. I might do that in next setup once current 520 kit is worn out.
 
#3 ·
It depends in what track you are attending. If the track is with wide and fast turns then the longer wheelbase will be a good thing. If your track has turns that need fast "turn in" then a shorter wheelbase is better.
I have read what AndyHP4 said but in the tracks that I attend are usually small without very fast turns and have not test those settings yet.

Also if you have the 10-11 bike with Alpha Racing pivot they suggest to set the rear shock to high position.
 
#6 ·
I think he meant that 2 links consist of the outer and inner link which could be considered one link depending on your brain.

I don't think losing one tooth on the back will be noticeable. I think stock is 46? So the change would be 46/45 X 100 for a percentage. Around 2 percent I think
 
#9 ·
FYI. According to Dave moss, every 4mm of lengthening in the wheelbase requires a 1 mm raise in the rear to keep the same angle and not allowing the swing arm angle to get too flat. -1 to the front sprocket is not going to change things that much. If you are worried about that little adjustment then start figuring out how many turns of preload(more or less than stock) you are in the front and rear and the exact diameter of the front and rear tires to determine the change in ride height etc. if you aren't riding at or near the top of the advanced group then those minor changes have little to no effect. I would try a proper suspension setup first


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#11 ·
FYI. According to Dave moss, every 4mm of lengthening in the wheelbase requires a 1 mm raise in the rear to keep the same angle and not allowing the swing arm angle to get too flat. -1 to the front sprocket is not going to change things that much. If you are worried about that little adjustment then start figuring out how many turns of preload(more or less than stock) you are in the front and rear and the exact diameter of the front and rear tires to determine the change in ride height etc. if you aren't riding at or near the top of the advanced group then those minor changes have little to no effect. I would try a proper suspension setup first
-1 front just caused wheel base to be longer. So would you leave wheel base longer like in pic? It works well for the straights and long sweepers.

I already have my sag setup properly. Did you mean something else to set up in suspension?
 
#10 ·
Okay, got the calculator out. Going from 17t to 16t is a 6.25% change. Going from 45t to 46t is a 1% change.
 
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#12 ·
The problem with trying to figure out your Geomerty settings is we have no idea what your preload is set too. If you have a lot of pre load in the front that makes the front ride higher, to little in the rear makes it ride lower and vise versa. Another thing is going from a 190 to 200 rear is going to raise the rear anyway. As an example. On Bridgestone going from a 190 to 200 is raising the rear by 4mm.

Generally speaking yes raising the rear will make the bike turn in better but there is a threshold at which if the rear is to tall turn in is sluggish as well as transition from side to side.

So 2 things have happened, your wheelbase is longer cause of the 1 down in front plus your rear ride height is increased from the tire size change. I would lower the rear to adjust for the raised rear height and see if that works. In general the BMW is nose heavy and raising the rear makes the front have to much weight and won't hold a line trail braking and to much weight won't allow it to turn well. It's a starting point and the easiest to try.
 
#14 · (Edited)
I'm ~185lbs with gear, 6' tall.
I have the front preload set with 3 full turns (only 5 lines show on tripple).
Rear with 1 one turn in. This puts me in middle of sag spec per manual.

What you say makes sense about not raising the rear. So it's still OEM height. Just to be clear, as far as I know it's only possible to raise the rear (not lower it) using the bolt on top of rear shock. I'm not talking about preload adjustments. Are we on the same page?

so without changing suspension. Bottom line, 5mm longer wheel base or shorter? Just looking for a balanced setup (street, track, twisties, etc...).

By only ~ 15/100 inch with the same chain pitch and number of links.

You are not going to feel this as a change in handling unless you race as an WERA expert.

You are also not going high 180's with a -1 sprocket unless you raised the rev limiter.

If you are having handling issues something else is going on. But keep in mind the S1000RR is not a quick turn-in bike in any event. It's strength is stability.

If you look at the swingarm in pic, my axle moved back about ~5mm.

I can tell you bike takes more effort to turn. It's more stable for acceleration and braking, but turn in became more difficult.
You know my unsmooth riding best on here :grin2: I still max 186mph on dash. With Sprint air filter, IAT relocation mod bike runs better/faster than stock. Being 185lbs geared helps.

So would you run with longer or shorter wheel base if you were in my shoes? I have a track day tomorrow, and I have a whole week of riding at Deals Gap soon. Many turns to go through, I'm leaning towards shorter wheel base.
 
#29 ·
Tough crowd. Jeez, fine 2 links.

@AndyHP4, thanks for the details. In USA we use 1.5 links :x

@Elk I get that. How do you explain my friend with stock gearing hitting high 180smph and I'm right next to him? As far as I know, the dashboard is limited to 186mph, but actual speed is more. Our dashboards are a mess. Did you see videos of RRs getting clocked by an external speed trap? Actually speed is higher than reported dashboard speed.

I decided to try shorter wheel base. Ordered master link. If I don't like it, I'll just go back to longer wheel base.

My next rear sprocket change will be coming up in few thousand miles, I'll also try +2. Luckily I have 17T front sprocket so I can test it. Just need to buy rear with +2.

Anyone runs with 118 links? How does it compare to 120 links?
 
#30 ·
The gauge cluster intentionally reads high. Subtract 8% from indicated speed to obtain the actual speed.

Or hit cruise, enter average speed, clear it, and wait for it to stabilize. This will display actual speed.

See, European Union Directive 75/443/EEC - Reverse and speedometer of motor vehicles

"4.4 The speed indicated must never be less than the true speed. At the speeds specified for the test in 4.3.5 above and between these speeds, there shall be the following relationship between the speed indicated on the dial of the speedometer (V1) and the true speed (V2):

0<= V1 - V2 <= V2/10 + 4km/h"
 
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