Ideal tire size combination. 110/150 vs 120/160. Wheel swap.

psych0hans

Member
Country flag
Hi guys, as I've posted before, I have an insane and unhealthy obsession of grafting a twin disc setup into any bike I own. To that avail I want to swap out the wheels of my RC with those of either an Aprilia RS250 or an older generation Ducati. I believe either combination will be lighter than stock, especially the rear. My dilemma is whether I should stick with the stock 110/150 tire ratios or should I switch to a 120/160 combo? I believe some people use 120 fronts on their stock wheels with good results, so wouldn't that be a better choice on wider wheels? I have the following options charted out -

  1. Aprilia RS 250 MK1 - 3" front 4.5" rear
  2. Aprilia RS 250 MK2 - 3.5" front 4.5" rear
  3. Unspecified Ducati - 3.5" front 4.5/5" rear

Please help me choose. I know this will only add weight to the bike and in possibly the worst place, but I'm doing this more to satiate my obsession than for any real performance gains. Also if I do it right, I might be able to keep that weight gain to a bare minimum or maybe even reduce the weight slightly. Titanium bolts/axles, lighter rotors, aluminium sprocket, etc, will all go a long way to reduce the rotating/unsprung mass, thus negating the effect(hopefully) of an extra front disc and calliper.
 
Last edited:

ToraTora

Member
Country flag
People that are running the 120/160 on the stock wheels are not getting what the think. Unless they only ride straight up, which might be a silly thing to do if you've bought a cornering bike!

Here's why. When you put a too large tire on the rim it effects the profile shape of the tire It goes from being a V shape to a U shape. Now when you lean a V shape tire you actually get a larger contact patch. That's really nice when you are turning. When you lean a U shape tire you get a smaller contact patch. So when you put the bigger tire on your wheel you get less cornering ability.

What's really funny is generally the folks that buy the too wide tires will not listen to this explanation. They have bought into the bigger is better. And well if straight up cruising is what you want to do it is true the too big tires will resist turning, but when you force them to turn they wont be nearly as useful.

So if you want the 120 tires get the wider rims. If you want the 110 tires get the less wide rims. With a bike as small as the RC you don't really need the 120 width, but you might choose that because of the significantly better tire selection available. 110s have a very limited selection.
 
Last edited:

psych0hans

Member
Country flag
Hi, thanks for your reply. I'll stick with the 3"/4.5" combo then with the MK1 wheels. Currently bidding on them on eBay, hope I get them...
 

Old3

Member
Country flag
I tried 120/150 on a Ninja 300 and conbos of those with stock at either end. Ended up back at 110/140 which i think is where the 390 should probably be too.
 

psych0hans

Member
Country flag
Have pulled the trigger on option 1) Aprilia RS 250 MK1 - 3" front 4.5" rear. Will post updates when I actually get the wheels, as they are currently on the way to my friends house in London. I'll hopefully pick them up in July. Unless he decides to be uber ultra generous and gets them with him when he comes to India this month, though that would be expecting too much :p
 

Sacape2

New Member
If it's purely for aesthetics, then go for it. I wouldn't expect any performance gain from it in anyway at all, even if there are any weight savings. As ToraTora mentioned, the contact patch will be different. I've read other threads where hard riders are having trouble making use of the stock 150 tires with about 1/2" of untouchable tread, saying that a 140 rear would be much more acceptable, making use of the entire contact patch. I can only see larger-than-stock tires being a larger expense by leaving even more unused tire tread.
 
Last edited:

psych0hans

Member
Country flag
If it's purely for aesthetics, then go for it. I wouldn't expect any performance gain from it in anyway at all, even if there are any weight savings. As ToraTora mentioned, the contact patch will be different. I've read other threads where hard riders are having trouble making use of the stock 150 tires with about 1/2" of untouchable tread, saying that a 140 rear would be much more acceptable, making use of the entire contact patch. I can only see larger-than-stock tires being a larger expense by leaving even more unused tire tread.

Hi, thanks for your reply. Yes, this is mostly for aesthetics, as I don't really expect to get any performance gains from it. Also, using a 150 rear won't be an issue as I will be upgrading to a 4.5" rear which will accept the stock 150 tire much better than the stock 4" wheel does. My only concern is trying to keep the front wheel as light as possible and I plan on achieving this with the use of Titanium bolts and hopefully a Titanium Axle, which I will fabricate. For the rear I will definitely switch to an aluminum 43T sprocket to reduce weight and get slightly taller gearing.I'll also be looking at sourcing lighter tires for the front and back once these wear out.

15_tireshootout_specs.jpg
 
Last edited:

psych0hans

Member
Country flag
Just to revive a dead thread, I'll be starting with this swap some time after next week. Will start off with the front, as that seems slightly less complicated and then proceed with the rear depending on how the front goes. I'll be using the RS250 axle on the front and machining spacers to accommodate it in the RC8 forks. Tire will be the stock 110/70 Metz M5. I've sourced a set of 110/70 & 140/70 street radial tires for the stock wheels till this mod gets done. Don't want to take her off the street indefinitely :eek:
 

psych0hans

Member
Country flag
Hi guys, after much ado, the deed has been done!!! The machinist at our factory fabbed up a new axle and spacers to accommodate the wheel and get it centered. Tomorrow I'll go and install the second brake disc. I have a set of brake lines that are too long for this bike, would that be a massive problem? It's meant for a Harley fat bob and has a "T" which will go above the fender.



s-l225.jpg
 

psych0hans

Member
Country flag
Updated pics, rear will go on by tomorrow.

Hi guys, I got the front end done a while ago, finally getting the rear also done. Weight savings of almost 3kgs over the original setup, will probably go down a bit once I count in the additional spacers, etc... which might be needed, but that shouldn’t be more than 2-300gms.
 

Attachments

  • C746182D-E031-4167-AE53-64177F1967B4.jpg
    C746182D-E031-4167-AE53-64177F1967B4.jpg
    232.7 KB · Views: 114
  • 0D84D00D-1BB5-4C56-9452-1BA845D1F2E9.jpg
    0D84D00D-1BB5-4C56-9452-1BA845D1F2E9.jpg
    237.4 KB · Views: 132
  • B6BBF4DE-B937-4AE1-8306-7FF6ECD8D309.jpg
    B6BBF4DE-B937-4AE1-8306-7FF6ECD8D309.jpg
    235.3 KB · Views: 118
  • 2614AACB-40BF-4311-A14F-99F528589D23.jpg
    2614AACB-40BF-4311-A14F-99F528589D23.jpg
    225.9 KB · Views: 112
  • 5D34C1FF-53E3-48EA-9B11-6F07DD89E69E.jpg
    5D34C1FF-53E3-48EA-9B11-6F07DD89E69E.jpg
    193 KB · Views: 100
  • 0C3F3EE3-5904-4D7D-8F9D-2157CB568B52.jpg
    0C3F3EE3-5904-4D7D-8F9D-2157CB568B52.jpg
    191 KB · Views: 110
  • E701C9B9-2F7D-46A9-94CB-AEBC2BBA870B.jpg
    E701C9B9-2F7D-46A9-94CB-AEBC2BBA870B.jpg
    194.4 KB · Views: 89
Top