Discussion about XR on 12s

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Discussion about XR on 12s

This is a discussion on Discussion about XR on 12s within the Mini-Motards forums, part of the General Talk category; OK so opening up the discussion as much as anything. But interested to hear some feedback. I got a really good deal on a set ...

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    Discussion about XR on 12s

    OK so opening up the discussion as much as anything. But interested to hear some feedback.

    I got a really good deal on a set of 12 inch wheels for my XR and got a chance to ride them a bit. The 12s setup consists of a 2.15 front and 2.5 rear and on TT93s and geared to match the gearing setup I had on the 16 in setup with BT45s.

    Couple of initial impressions, bike actually seems more stable at lean but twitchier when changing directions from being mostly upright. I can get pretty much right to the edge of the tires and profile looks good and feels pretty stable on the edge of the tire. Bike seems to punish you a lot more with movement if your inputs are not really smooth compared to the other setup but less "moments" if you push it a little. Drum brake seems alot better on the small wheels, acceleration seems a bit snappier.

    Here is the gripe. Track is a .6 mile track and my lap times were in the 56 sec range on the 16s and after several hours of track time over a couple days I could only seem to run in the 58s on the 12s. Ground clearance is an issue but riding road race style and trying to get off the bike it could be minimized so only barely scraping pegs in a couple corners.

    Is there anything inherently difference about riding the 12s that I should be taking into consideration. To be honest I expected the bike the be a little faster from reducing the rotational inertia and figured the TT93s would be better than the BT45s in terms of grip.

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    T-Wrecks Racing's Avatar

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    You should run 12" Mitas tires in soft or SS, way better than TT93s. I almost killed myself with those.
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    tt93's are agreat tire but that isn't the issue, what kinda suspension do you have and isit set-up correctly? Granted mitas arepmt’s are a far superior option

    Also justdropping topping to 12’s isnt really going to make the bike faster, the 12’sare still heavy

    my endurance team runs an xr100 on 12's, I have also ridden one on 17's and16's so here’s my take


    17’s are greatfor larger tracks and are more stable, 16’s are great for the budget to see ifyou like racing but if the rules for the classes you race in there isn’t reallya reason to keep them. 12’s are greatfor small tight kart tracks, the bike it more “twitchy” but it opens up so manymore opportunities for different lines and the ability to change lines quickerand easier than with 17’s
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    I have typical XR suspension on a budget lol. Modified springs with progressive section removed and spaced and preload with PVC spacer and 20wt fork oil at 100mm air gap collapsed. Rear is a Tak rear shock with upgraded spring. Setup is the same on the 12s as it was the 16s. I have ridden Ashley's bike for a couple laps and the CR80 front end swap he has was MUCH nicer but that upgrade will be while unfortunately. I do think after thinking about it for a while that ground clearance (and lack of it) was probably reducing confidence a bit. I had the forks pulled up through the triple as far as they could go until they touched the bars but since have pulled them down flush to get a bit more ground clearance as and am swapping over the newer style linkage and swingarm since I have one sitting here to get a bit more ride height in the rear (its not much but hey, I'll take what I can get).

    I do think that 12s are "better" in the long run once I get used to them and get the bike setup to get the most out of them. But I was certainly more comfortable and faster on the 16s with the 'stones.

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    Like you said,you just gotta get used to it.. Becareful just raising/lowering the folks without doing the same in there rear,it will screw with the geometry of the bike. I prefer the front to be alittle lower to have better turn in but itwill cause the bike to be even twitchier, having the front higher than the rearwill cause you to run wide on exit.

    The tak shockis better than a works, those things a pogo sticks, lol. Of course the way to go is ohlins but it’snot “budget” friendly
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    ^^ yeah its a little bit of the lesser of two evils at them moment. The forks were raised up through the triples before as I like my bikes a little bit more on the nose for the same reason (quicker turn in) but also to try and get some weight over the the front of the bike to keep the front tire working. But I think getting the bike up a bit to get some ground clearance is high on my list at the moment so I dropped the forks back down. That and by switching to the newer style linkage I gain a bit of rear height as well to counteract the change in the front.

    What I really imagine I should do is get the weight distribution front to rear with the "old confidence setup" and then have a data baseline (can't easily use height to hard parts because of the diameter differences with wheel/tire, well I guess I could if I took some time to measure well) but I don't have appropriate scales to do so.

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    Wrench's Avatar

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    I cut the steering head off my X4 motard (on 12's) and rewelded it with the front raked out several degrees to make the front more stable/less twitchy. Worked great! I did this halfway through the race season last year. It really helped all around, especially on the larger tracks. During the alignment process, I also discovered that the steering head was not welded on straight from the factory, so it helped in more than one way.

    One of the major issues has to do with the trail. To run the 12's, the dirt bike geometry is not ideal. Rake would be in the ballpark if they had forks that placed the axle further back (like directly on the bottom of the forks, as opposed to on the leading side of the forks).

    Weight distribution on a mini bike (the bike weight itself) is barely even a factor. Your body weight and positioning have WAY more effect on weight distribution than anything else. Move the bars as far forward and as low as possible, and keep your body weight on the pegs.
    Paul
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