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# Technical Q&A with Lennard Zinn – Straight rake? Stuck on you

## Straight blades?Dear Lennard,Thanks for the discussion on rake and trail and various geometry issues in your December 21st column. I have a follow-up question: Since it appears you can achieve trail change via head tube angle and fork geometry, what are the implications of a straight fork like a Colnago Star, versus a fork that has blades that curve as they near the axle?Jeffrey Dear Jeffrey,I should have put something about this in the book, because it is such a common misperception. Straight forks do have rake (i.e., offset of the front hub from the steering axis)! Look at your

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By Lennard Zinn

Technical Q&A with Lennard Zinn – Straight rake? Stuck on you

Photo:

Technical Q&A with Lennard Zinn – Straight rake? Stuck on you

Photo:

Dear Lennard,
Thanks for the discussion on rake and trail and various geometry issues in your December 21st column.

I have a follow-up question: Since it appears you can achieve trail change via head tube angle and fork geometry, what are the implications of a straight fork like a Colnago Star, versus a fork that has blades that curve as they near the axle?
Jeffrey

Dear Jeffrey,
I should have put something about this in the book, because it is such a common misperception.

Straight forks do have rake (i.e., offset of the front hub from the steering axis)! Look at your suspension fork on your mountain bike. It achieves it usually by a combination of a forward-swept fork crown and forward-offset dropouts (original RockShox forks angledthe legs at the crown). The Colnago Star fork, like Colnago’s earlier straightsteel forks has forward-angled legs coming out of the crown that are notcoplanar with the crown and steering tube, in order to create offset. Itsrake is similar to that of any standard carbon road fork (i.e., 4.2-4.5cm).

You can see in the accompanying photos that other straight forks likethe True Temper Alpha Q straight-blade road fork (top right), which has 4.4cm of rake, and the Surly Instigator suspension-corrected rigid MTB fork (above left), which offers 4.3cm, have fork legs angled forward where they attach to the steering tube.
Lennard

Does Chris work with Tulio?
Dear Lennard,
Are you aware of a way to run Campagnolo 10-speed on a Chris King rearhub? One idea I proposed was to use an asymmetrical rear rim. This is becauseon the CK website they site concern about the chain, while in the largestcog, riding too close to the drive side spokes.
Jason

We have looked into the Campagnolo conversion kits that areavailable. With the cog center-to-center spacing being wider than the Shimanocog center-to-center spacing, the extra width ends up on the inboard sideof the cassette. This reduces the amount of clearance the chain and derailleurhave before coming in contact with the spokes. Customer feedback has generallybeen positive with regards to the usage of the American Classic 10-speedCampagnolo conversion kits. We have not received adequate feedback regardingthe Wheels manufacturing cassettes. When using these kits a properly adjustedderailleur is very important. With the tight tolerances between the derailleurand the spokes, a misadjusted limit screw could throw the derailleur intothe spokes. Clearance can be effected by the size of the largest cog, thebigger the cog the better the clearance. Spoke gauge, lacing pattern andrim selection may also have an effect on clearance.
Tech/Warranty
King Cycle Group

Help! My wheels are eating my bike!
Dear Lennard,
I’ve got this odd problem that only one person I’ve met so far hasever heard of before. The axle threads of my rear hubs are slowly chewingthrough the drive side dropout on both of my Cannondale frames (mountainand road).

I’ve always tightened the Shimano skewers as tightly as possible. I’measily over 250 pounds, but have the leg power to push huge gears and ridevery rocky terrain. A former sponsored rider said he ran into the sameproblem before switching to cartridge bearing hubs. Unfortunately I cannotafford such expensive hubs and am trying some ideas. I’ve tried using steelreinforced epoxy to fill in the frame and axle threads but the epoxy quicklycrumbles away. I’ve thought of filing off the axle threads, but am worriedthis could cause other problems. Or is there anyway to create a thin steelshell around the axle to protect the frame?
Jake

Thanks for the opportunity to answer this question. With closeto 3 million Cannondale frames produced to date, this is an extremely rareissue that we have not run across in the last few years. A threaded steelaxle is very hard and abrasive compared to any aluminum frame dropout,and if the quick release skewer was slightly loose at just one point inthe frame’s life, the axle could certainly move and cause the initial damageto the dropout.

Once this initial damage that enlarged the axle slot in the dropouthas occurred, it is extremely difficult to prevent the axle from movingand causing more wear, even if the skewer is very tight.

Hubs that use cartridge bearings are now very common in the bike industry,and their price has come down such that Cannondale is able to use themon our entry level bikes. The aluminum axle ends of these hubs are muchless damaging to the dropout if the bike is ever ridden with a slightlyloose quick release.

Cannondale does offer a discounted frame exchange program for wear &tear & damage issues, such as yours, that do not fall under our lifetimeframe warranty. Thanks for choosing Cannondale frames for your adventuresthrough the French Alps!
Chris Peck
Director of R&D
Cannondale Corp.

Stuck on OCLV
Dear Lennard,
I have an American Classic two-piece aluminum seatpost stuck in myTrek OCLV frame. In trying to remove the post I succeeded in twisting theseat clamp but the post remains stuck. Have I diminished the integrityof the seatpost? And is cutting it out the only alternative left?
Gene

Dear Lennard,
Help! My Dura Ace seatpost is hopelessly stuck in a Trek OCLV frame.I was told not to lube the post because of the carbon seat tube, but nowthe post won’t budge due to accumulated sweat, corrosion, and who-knows-what-else.Is there anything I can drip down there to loosen things up? How aboutheating it up with a hair dryer or something? I’m prepared to sacrificethe seatpost at this point if that’s what it takes.

(After an email interchange):
Thanks for these tips. As it turns out, I tried penetrating lube (LiquidWrench) to no avail. I also took it to my local Trek dealer who was unableto get it out. Progress eluded me until I “crossed the Rubicon” and madethe decision not only to sacrifice the Dura-Ace seatpost, but that I waseither going to get the post out or destroy the frame in the process. Therest of the story involves an unsightly cast of characters, including ammonia,three hack saws, laborious lengthwise cuts in the post, a vice, a hammer,and two destroyed screwdrivers which were doubling as chisels. EventuallyI was able to remove the post through a combination of (interior) hacksawcuts and chiseling. The frame appears to be okay, but it was quite an ordeal.

I never had a problem like this with steel or titanium frames becauseI always kept my post well greased. I can’t do this with the Trek OCLV.The frame rides well, but I can’t help but wonder if there isn’t a betterway to design the seat tube sleeve to avoid these problems. Perhaps aninner metal sleeve? My dealer told me that the only way to avoid this inthe future is to take out the post quite often and clean it and the tube.
Ralph

Dear Lennard,
For this one, we went to Jim Colegrove, our head carbon engineer:
First try: Any high performance penetrating oil will work. Howeverit may take some time. Take out the Bottom Bracket and with the bike inverted,pour a “large” quantity of the penetrating liquid into the seat tube. Thiswill attack the problem from the bottom. Let it work for a while; thismay take days.
Second try: (if the oil did not work) Using a heat gun (nevera torch of any kind) heat and cool only the seatpost several times; thiswill help to break up the corrosion. Do not try to pull the seat post whenit is hot. You could also try using an ice bath to cool the seat post orstick the whole bike into a freezer both of which will shrink the seatpost away from the carbon seat lug insert.
Last resort: The bike could be sent back here to Trek and wemay be able to free the post with out destroying it or the frame. Checkwith your local retailer for details.
Dean Gore
Trek Bicycles