Bike angle/optical illusion
#1
Senior Member
Thread Starter
Bike angle/optical illusion
It seems my bike has a bit of a slope from rear to front. Is this normal? I haven't noticed that anywhere else...
#2
Senior Member
Join Date: Nov 2014
Location: Eugene, Oregon, USA
Posts: 27,547
Mentioned: 217 Post(s)
Tagged: 0 Thread(s)
Quoted: 18376 Post(s)
Liked 4,511 Times
in
3,353 Posts
The first thing to do is to put it on a hard surface, and simply measure ground to top tube.
A back to front slope top tube is rare on bikes, other than "Funny Bikes" which would have a much more pronounced slope.
Are the tire/wheel sizes both 700c, and reasonably close in size (not 27")?
Does the black paint on the fork match the black paint on the head tube?
A back to front slope top tube is rare on bikes, other than "Funny Bikes" which would have a much more pronounced slope.
Are the tire/wheel sizes both 700c, and reasonably close in size (not 27")?
Does the black paint on the fork match the black paint on the head tube?
#3
Senior Member
Join Date: Mar 2014
Location: City of Angels
Posts: 4,870
Bikes: A few too many
Mentioned: 42 Post(s)
Tagged: 1 Thread(s)
Quoted: 1364 Post(s)
Liked 2,181 Times
in
1,183 Posts
RC,
The bike appears to be at an angle to the rear wall, causing the appearance of the sloping tube...as mentioned best to check with a tape.
Best, Ben
The bike appears to be at an angle to the rear wall, causing the appearance of the sloping tube...as mentioned best to check with a tape.
Best, Ben
#4
Senior Member
Join Date: Sep 2005
Location: Oakland, CA
Posts: 3,265
Bikes: '82 Univega Competizione, '72 Motobecane Grand Record, '83 Mercian KOM Touring, '85 Univega Alpina Uno, '76 Eisentraut Limited
Mentioned: 57 Post(s)
Tagged: 0 Thread(s)
Quoted: 1088 Post(s)
Liked 1,205 Times
in
701 Posts
Yeah, looks like your front wheel is a bit farther from the wall than the rear, which could be producing the illusion. Like mentioned above, maybe your front tire is a slightly smaller width/diameter than the rear. Nothing looks out of alignment, and this bike would have had a straight top tube, not angled.
#5
Senior Member
Thread Starter
The back tire is a 1/4 taller. And it appear that accounts for the difference.
#6
Bike Butcher of Portland
Join Date: Jul 2014
Location: Portland, OR
Posts: 11,639
Bikes: It's complicated.
Mentioned: 1299 Post(s)
Tagged: 0 Thread(s)
Quoted: 4682 Post(s)
Liked 5,800 Times
in
2,284 Posts
There’s nothing sacrosanct about having a perfectly level top tube. When I rerake front forks on vintage bikes, the front end typically drops a few mm. Almost no one notices unless I point it out.
#7
Edumacator
Join Date: Jan 2018
Location: Goose Creek, SC
Posts: 6,807
Bikes: '87 Crestdale, '87 Basso Gap, '92 Rossin Performance EL-OS, 1990 VanTuyl, 1980s Losa, 1985 Trek 670, 1982 AD SLE, 1987 PX10, etc...
Mentioned: 59 Post(s)
Tagged: 0 Thread(s)
Quoted: 2439 Post(s)
Liked 3,128 Times
in
1,967 Posts
Profile of the different tire might account for a bit.
#8
Shifting is fun!
Join Date: Aug 2009
Location: South Holland, NL
Posts: 11,006
Bikes: Yes, please.
Mentioned: 280 Post(s)
Tagged: 0 Thread(s)
Quoted: 2198 Post(s)
Liked 4,601 Times
in
1,764 Posts
Not all that unusual. Giant did it:
#9
Senior Member
Join Date: Jan 2004
Location: Madison, WI USA
Posts: 6,154
Mentioned: 50 Post(s)
Tagged: 0 Thread(s)
Quoted: 2363 Post(s)
Liked 1,749 Times
in
1,191 Posts
Whiskey tango, no one suggested putting a LEVEL on the top tube?
My vote is for the tire.
My vote is for the tire.
Likes For madpogue:
#10
Senior Member
Thread Starter
Likes For roadbikeChris:
#11
framebuilder
It is not uncommon for a classic custom frame to have a top tube that is not level. I got an Italian made Masi in Milan in 1972 ($350 all Campy including the brakes). The top tube is off by a about 6mm. Others that owned Masis on the Classic Rendezvous list started to check how level their top tubes were and the range was anywhere from 3 to 9mm off.
#12
Senior Member
Join Date: Mar 2014
Location: City of Angels
Posts: 4,870
Bikes: A few too many
Mentioned: 42 Post(s)
Tagged: 1 Thread(s)
Quoted: 1364 Post(s)
Liked 2,181 Times
in
1,183 Posts
#13
Senior Member
Thread Starter
The floor on which I had the bike when checking level, is level.
Likes For roadbikeChris:
#14
Senior Member
Speaking of level, I would suggest that the handlebar woes you mentioned on the other thread may have a lot to do with your saddle angle. I would level that out and ride some more before going nuts with the bars.
Likes For due ruote:
#15
Senior Member
Thread Starter
Last edited by roadbikeChris; 10-10-19 at 05:53 PM.
#16
(rhymes with spook)
Join Date: Aug 2009
Location: Winslow, AR
Posts: 2,788
Bikes: '83 univega gran turismo x2, '85 schwinn super le tour,'89 miyata triple cross, '91 GT tequesta, '90 yokota grizzly peak, '94 GT backwoods, '95'ish scott tampico, '98 bonty privateer, '93 mongoose crossway 625, '98 parkpre ariel, 2k'ish giant fcr3
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 919 Post(s)
Liked 745 Times
in
546 Posts
too many variables have to be accounted for that level to even be an accurate representation.
#17
Senior Member
Join Date: Jan 2004
Location: Madison, WI USA
Posts: 6,154
Mentioned: 50 Post(s)
Tagged: 0 Thread(s)
Quoted: 2363 Post(s)
Liked 1,749 Times
in
1,191 Posts
And yes, fore-aft position is a significant fit factor. You can also look for a seat post with more or less setback.
How many is "too many"? The floor? The tire profile? Tire pressure? Seismic activity? Granted, a measurement on a non-carpeted surface would be marginally better, but the OP's finding is enough to confirm that it's not an optical illusion.
Last edited by madpogue; 10-10-19 at 05:53 PM.
Likes For madpogue:
#18
(rhymes with spook)
Join Date: Aug 2009
Location: Winslow, AR
Posts: 2,788
Bikes: '83 univega gran turismo x2, '85 schwinn super le tour,'89 miyata triple cross, '91 GT tequesta, '90 yokota grizzly peak, '94 GT backwoods, '95'ish scott tampico, '98 bonty privateer, '93 mongoose crossway 625, '98 parkpre ariel, 2k'ish giant fcr3
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 919 Post(s)
Liked 745 Times
in
546 Posts
no need to be snarky. i've built alot of walls. so, yeah, the floor, the carpeting thickness, the tire pressure and/or actual size, actual level of foundation even. and, a small tiny level like that is very sensitive to variation compared to a longer tool. the better way to really determine would be a measuring square; top tube against the dropouts.
i'm not saying the top tube is or isn't level, btw. i'm just commenting on the method
i'm not saying the top tube is or isn't level, btw. i'm just commenting on the method
Likes For thook:
#19
Senior Member
Thread Starter
I think I will take the bike to the bike shop tomorrow and get it on a level floor and recheck it. The rear tire is 1/4 taller than the front. And the level I used bears that out. I don't want to create a lot of controversy here.
#20
Senior Member
Cumulative error?. Your rims appear to be differing types as are your tyres? Yes?
Image perspective may not be square on?
Unless it is a 'funny bike' for a sideshow all slight variables can be compensated for with height/angle adjustment.
Why to the bike shop?
Does it ride well, no dropping to one sides, keeps a straight line?
Save yourself some time, money and possible jesting(?).
Do you have a tape measure?
If you are wanting some perfection, use Pythagoras (3,4,5) to check for square (or a square, or level).
You do not require a perfect level surface; a 180 degree flat surface is all you require.
Last edited by slow_runner; 10-10-19 at 06:34 PM.
#21
(rhymes with spook)
Join Date: Aug 2009
Location: Winslow, AR
Posts: 2,788
Bikes: '83 univega gran turismo x2, '85 schwinn super le tour,'89 miyata triple cross, '91 GT tequesta, '90 yokota grizzly peak, '94 GT backwoods, '95'ish scott tampico, '98 bonty privateer, '93 mongoose crossway 625, '98 parkpre ariel, 2k'ish giant fcr3
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 919 Post(s)
Liked 745 Times
in
546 Posts
well, level or not top tubes are pretty controversial
#23
The dropped
Join Date: Oct 2018
Location: Columbus, OH
Posts: 2,144
Bikes: Pake C'Mute Touring/Commuter Build, 1989 Kona Cinder Cone, 1995 Trek 5200, 1973 Raleigh Super Course FG, 1960/61 Montgomery Ward Hawthorne "thrift" 3 speed, by Hercules (sold) : 1966 Schwinn Deluxe Racer (sold)
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 1739 Post(s)
Liked 1,014 Times
in
696 Posts
Likes For Unca_Sam:
#24
Senior Member
Thread Starter
#25
Senior Member
So to eliminate error requires a better level or as a 'need must' the level needs to be reversed and viewed again.
Regardless a levels amount of response or rated accuracy, always confirm the level is indeed an accurate one by reversing the level and ensuring the bubble has not shifted.
End of amateur instruction lol.
Last edited by slow_runner; 10-12-19 at 07:07 PM.
Likes For slow_runner: