Jump to content

Tire Size


Recommended Posts

I have an F4i. It comes stock with a 120/70/17 front and a 180/55/17 rear. I've had some tire problems(nails and such) and money problems (none to replace tires with holes) I got an almost new 190/50 from one buddie and another almost new 120/60 from another buddie. I put the rear tire on a month or so before the front tire and the rear felt okay. No handling problems to speak of. I put on the 120/60 front the other day and ...........well I low sided it about the third day. It felt a little different on corner entry (diving very aggresively) but I thought I was handling that okay. It happened so fast that I didn't even know what happened . My question is: Would the tire change on the front change the setup drastically enough to cause this lowside or did I just slip on something? Or did I jsut screw up my entry that bad. I'm an aggresive street rider. I slide the bike in and out of turns all the time but, this was different. Like I said: down fast and wonderin' "What the haell just happened?"

Link to comment
Share on other sites

Tire spec's are expressed as a fraction called aspect ratio. Width/percentage of width.

 

180/55 means 180mm wide by 55 percent of that figure tall. Or 99mm.

 

When you swapped the rear you lost about 4mm ride height at the rear. Significant but not huge.

 

However, when you swapped the front you lost about 12mm of ride height at the front. BIG difference.

 

So, yeah, definitely changed the geometry. Overall loss of 8mm at the front. No doubt it felt different.

 

Overall geometry effect would be steeper steering angle. Quicker turning and less stable at the front.

 

Additionally, both tires being lower profile would also feel different. Whether it would significantly change the contact patch or flickability I can't say without intimate knowledge of said tires' construction/characteristics. Which raises another question. Were the "new"-er tires matching brand/model? Were they the same as the one's that came off? There's more than size to consider there re: handling characteristics.

 

Anyway, I can't say this caused you to fall down. Maybe you just hit a slick spot. But all things being equal, it would certainly have changed the handling characteristics.

Link to comment
Share on other sites

Just to clarify. Yes, they were the same brand. Pilot Power ZR 17's. Anyway, I went back and looked the area over in the daylight and found a spot of unfinished cement like it fell off the back of a truck from another pour. You know like a pile of poop from a rock dog. I've been around that corner plenty but, I always keep my lane. That night I cut to the inside and I'm pretty sure that pile of rocky dog poop coupled with the change in bike setup did me in. I'm alright so's the bike, just a little buggerd up. So is the bike. I did the math too, but I couldn't raise the front anymore. The forks are topped out at the triple clamp. I've got vortex clipons and the only thing above the clipon is the fork cap nut. I'm putting on a 180/55 tonight and as soon as I can, a 120/70 back on the fornt.

Link to comment
Share on other sites

Glad you are OK dude. Sorry I didn't ask before. Anyway, I don't mean to say that the changes you made were wrong or bad. Only to indicate that those changes would more than likely make the bike feel different. Some people change ride height quite a bit from "stock". And run different size tires than what came on the bike. I don't mean to imply that you should lose the newer tires. And realize that going back to a 180/55 while keeping the lower profile front will effectively decrease the front ride height a full 12mm. Instead of the 8mm you have now. I'm all for experimenting. It's my opinion that many bikes need more rear ride height or steeper steering. All I say is be aware and be prepared. Good luck!

 

And watch out for those rock dogs!

 

PS I'm thinkin' lotsa folks probably run F4i's at the track and might have much more bike specific info about how they might alter geometry or what size tires they run. Any help out there?

Link to comment
Share on other sites

  • 2 weeks later...

Thank's for the replies. Still have the 190/50 on the rear and changed the front to the original 120/70. WIERD It seemed fine before but, is very wierd now. Hard to turn in. feels like front wants to push out or slide out ( need to get my lingo down pat) When I originally went to the 190/50 rear it felt great!! as in faster than ever. Now it feels...... well, wrong. So I lowered the front 3mm. helped a little......I guess. Gonna try another 2mm's and I'm working a deal for a 180/55 right now. I mean right now on the Yahoo IM. Hang on a sec while I reply to my reply. Ha! No deal on the 180 so anyway.......... Hey! Where's Jef4y? He's probably a plethora of info on this particular bike. And thanks again for the input. Man, I love this place!

Link to comment
Share on other sites

post-880-1137318985_thumb.jpgpost-880-1137318819_thumb.jpgWould ya'll like to hear more about the crash? I thought so. But first, save the "Idiot lectures"....Ahh! never mind. I can't stop you and another "You stupid, ignorant, moronic idiot what were you thinking?" lecture or two certainly couldn't hurt as much as, or should I say, do as much damage as, a crash like this could've. (friends, family, 20 year marraige, 15 year old son and 10 year old daughter.) BTW I never told my family just a few close riding buddies. Neutral chamber, brushed concrete, slightly decreasing left hander @ 50. I take this turn all the time but, well you know the story. I take it in my GMC 1 ton van at 20 or 25 holding my lane and not squeeling anything. Like I said, I was on my butt so fast, it had to be something other than rider input. There was absolutely no warning. I never even puckered up! Arai has, once again, saved my life. There was a parked semi around and down the way a bit and well.. you get the picture. I bounced off the ground flipped around back first and into the rear end of said tractor trailer, leading with the back of my Arai Signet GT. Folding me up and back on the pavement for a third impact with the rear wheels( No wait....pavement, head in trailer, pavement and then wheels) so that would be the fourth impact and then pavement and slide to a stop. On a track this would've been a laughable crash at best. I'ts all funny till someone gets hurt. And that's why I'm telling it. Knee dragging is for the track! I can't wait for the new season. My track, "The Motorsport Ranch" in Ft. Worth,Texas just added 2.7 miles to go from a 1.7 mile technical to a 4.4 mile multi-track.....uh, track! I can't wait! I don't race.....yet but, sure would if someone could afford it for me. Pics of the Arai, and the new paint job. I do the body work and paint myself. Not quite factory but, looks real good at 60.
Link to comment
Share on other sites

i'm sorry. jef4ry can't answer just now. he's outside shoveling snow. please leave a message...beep. :lol:

 

oh it's nice to live in texas where the sunshine never stops, i reaaly wanna go there but i can't afford the cost.... (sung to the tune of yellow rose of texas) :P

 

silly sunday. get a sponsor. visa/mc/amex/discover are NOT sponsors... :D

Link to comment
Share on other sites

wow. yeah, you never told us about the semi either...

 

actually, i hate to say this, the image is kinda hilarious the way you describe it. (pavement, head in trailer, pavement, wheels) reminds me of the highside description we hear at the track...all i saw was sky, ground, sky, ground, sky....as one who has been there...i'm, um, laughing. really glad you're alive to tell funny stories about it and brush it off.

 

i refuse to hand out marital advice on a mc website, but speaking from experience...um, i don't think that story will help your cause come spring when you try to explain that you are going to spend thousands of dollars to go ride SUPER FAST on a BIG RACETRACK because it's so much safer than the street. well, then again, maybe it would help. but weighing the value of telling now against being the bad guy for hiding it if you wait til spring....double bind. you're on your own mate. :D

 

i do manage to convince most people that tracks are safer than the street because:

 

1. everyone is going the same direction.

 

2. everyone has gone to school and been tested and supposedly has a good grip on what we are doing.

 

3. it is a closed course. no little old ladies crossing the street in front of you or semi trucks parked on the curb. no mailboxes to hit if you run off course. (my favorite street target)

 

4. it is a controlled environment where nothing changes from lap to lap. and when something does change, there are flaggers to communicate the type and severity of change before you get there.

 

5. all machines must pass strict tech inspection each time. and are safety wired for most anything that can fall off or leak.

 

6. and, of course, if you do fall down hard enuf to say ow, there are generally at least two ambulances, paramedic emt's and maybe even a helicopter on site no more than 30 seconds away.

 

etc.

 

though i still get the family members who look askance at me like i'm trying to justify/rationalize a death wish or think of racing as something akin to drug addiction.

 

"wow. must really be a big RUSH going so fast." (you might as well b sniffing glue)

 

well...yes and no. not really in the way one might think. on the one hand, yes, the first time irode a ninja w keith at watkins glen (bloody fast track) wiht no chicane back in those days, i nearly collapsed after my first session i was shaking so hard from adrenalin. indeed, taking a few fast corners on your favorite backroad doesn't even begin to prepare one for the experience of trying to go AS FAST AS YOU POSSIBLY CAN, AS CLOSE TO CRASHING AS YOU POSSIBLY CAN BRING YOURSELF FOR SAY 30 MINUTES.

 

However, just like driving the interstate for the first time, that feeling goes away and you get used to the speed. it becomes normal. i remember the first time i drove at 55mph it felt like warp speed. after a while i was cruising at 85 like nothing. right? slow down to 55 and it feels like you can hop out and jog next to the car.

 

anyway, the rush for me now is the attempt at perfection or the high of getting it right and knockng tenths of a second off my laptimes. about the same high i get playing a beethoven sonata on the piano.

 

anyhow, i don't know what that has to do with the price of tea in china but...i felt like a little ramble. B)

Link to comment
Share on other sites

  • 2 weeks later...

Nice of you to ramble mate! Yeah! Sky, ground, sky, ground! Tuck and roll beotch! Still not tellin the misses though. I found out the other day from a neighbor that she has a pretty good idea about what happened. (both times) He said she told his wife that I've been trying not to show that I was hurt and that she noticed that my bike was banged up. then a few days later it had fresh paint. Ha Ha Ha!!!! Still not tellin. It got knocked over by some a-hole in a parkin lot. That's my story and I'm stickin to it. Oh! And the mattress hurts my back, and my shoulder and my bum and gives me a three week headache. Lucky she hasn't asked about the scuffed up leathers hugh?

Link to comment
Share on other sites

yeah, i hate to admit it but most of the time the only person we manage to fool is ourselves. it's her job to know and to let you think she doesn't know. kinda like my grandma used to do with grandpa's bottle of hootch under his workbench when i was a kid. i think it was the sneaking for a bit of being bad and damn the rules that meant more than the buzz. in anycase, she never let on and everyone was happy. it's a rare woman that can not only accept a man but appreciate or enjoy the boy. especially in this age of ...um, motrcycles. that's what we're talking about. motorcycles. ahem...so...as i was saying...are you protecting her from worrying or yourself from hearing bout it....haha. both? works for me.

 

anyway, really sorry to hear about the three week "headache". chances are that'll piss her off more than anything else. chances are she could care less about the paint job...as opposed to the ...uh, nevermind. there i go again. get well soon dude. keep the shiny side up, or the sticky side down or ...hell, do whatever you want. frankly ive had some of my most interesting experiences four paws in the air...learned most of my fabrication skills sequel to the sky ground event... :D

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...